The demand for high data throughput leads to development and utilization of various novel radio communication systems operating in the millimeter wave range. It is associated, on the one hand, with a wide frequency bandwidth available for use in said range, and on the other hand, with significant technological advances made over the past few decades, allowing to create modern, effective and cost-efficient (in terms of large-scale production) transceivers operating in frequency ranges from 30 GHz to over 100 GHz. Modern millimeter wave radio communication systems include, without limitation, point-to-point and point-to-multipoint communications, car radars, wireless local area communication networks, imaging and surveillance systems, etc.
The effectiveness of millimeter wave communication systems is determined largely by characteristics of antennas used in said systems. Such antennas generally should have a high gain value, and consequently, should form a narrow radiation pattern beam. In this case, the antennas provide effective (i.e. with maximum throughput) signal transmission over long distances.
The requirement for high gain value is determined by a small wavelength of radiation in millimeter wave frequency range, which leads to difficulties in transmitting a signal over long distances using antennas with insufficient gain values. Furthermore, in said frequency range, the effect of weather conditions and athmospheric absorption is high (e.g., in the frequency range of about 60 GHz, the effect of oxygen spectral line absorption is high, leading to additional signal attenuation of 11 dB/km). This absorption can be compensated only by using high gain antenna systems since the emitted power level is generally limited by the regulation requirements and transceiver performance.
However, the use of antennas with a narrow radiation pattern beam involves difficulties related to antenna alignment and probability of connection refuse in case of even small orientation changes of the antenna mounting structure. It is also important to provide automatic initial alignment in the system deployment procedure that reduces the deployment time and costs. In order to provide automatic alignment of the beam direction in a certain continuous angle range (with the width of several main radiation pattern beams) at short time without the need of special staff service, aperture antennas have to provide electronic beam steering capabilities. In other millimeter wave applications, such as radars or imaging systems electronic beam steering feature is also needed in order to exclude mechanical rotation motors and to improve processing time and system endurance.
Traditionally in lower frequency ranges to resolve the above-mentioned problem of providing electronic beam steering, phased antenna arrays are used. With the evolution of semiconductor technology such kind of antenna arrays became feasible even in millimeter wave range. For instance, there are several companies and research groups around the world who are developing or already supplying MMIC receivers, transmitters, and transceivers in 60 GHz range for the new generation of Wi-Fi systems supporting IEEE 802.11ad standard. These MMIC transceivers have up to 8-32 independent outputs with the controlled phase of a carrier signal [see, for example, Cohen, E.; Jakobson, C.; Ravid, S.; Ritter, D. “A thirty two element phased-array transceiver at 60 GHz with RF-IF conversion block in 90 nm flip chip CMOS process”//IEEE Radio Frequency Integrated Circuits Symposium (RFIC), 2010]. Consequently, a phased antenna array of 8-32 elements can be realized. Classical representation of phased array system is shown in FIG. 1. It is important that any beam position in a continuous angle range can be formed depending on the phases on each antenna element provided by phase shifters, thus, this system is capable for adaptive beam scanning
Another prior art antenna array system (known from Cetinoneri B.; Atesal Y. A.; Rebeiz G. M., “An 8 8 Butler Matrix in 0.13-um CMOS for 5-6-GHz Multibeam Applications”//IEEE Transactions on microwave theory and techniques, Vol. 59, No. 2, February 2011) is shown in FIG. 2. It is based on single transceiver, a switching system and a Butler matrix. The Butler matrix is a type of passive reciprocal beam-forming networks and it has N switched inputs and N phased outputs. Depending on which of N inputs is accessed, the predefined phase law is formed on all matrix outputs and, thus, antenna beam is steered in a specific direction in one plane. Other important properties of a Butler matrix include:                1. Switched inputs are isolated from each other;        2. Signal phases on N outputs are linear with respect to position, so beam is tilted off main axis;        3. None of the inputs provides a broadside beam;        4. The phase increment between the outputs depends on which input is used.        
Described switched-beam antenna array apparatus with a beamforming network is considered as the closest prior art for the current invention.
In the example shown in FIG. 2 matrix size is 8 by 8 that allows forming 8 beams in different neighboring directions. This communication apparatus is beam-switching rather than adaptive beam-scanning system shown in FIG. 1. However, the advantage is that it requires only one transceiver. Other matrix and antenna array size can be used, for example, N=4 or N=16.
One practical realization of an 8 by 8 Butler matrix is shown in FIG. 3. It includes 90° hybrids (or 3 dB couplers), fixed phase shifters, and crossovers. All these elements are known from the prior art and can be used for millimeter wave applications. For example, 90° hybrids can be realized as branchline couplers, Lange couplers, or other coupled line couplers, or in the case of waveguide, as the Riblett coupler.
It is well known that in both described antenna arrays the distance between antenna elements should be about half of an operating wavelength to eliminate grating lobes in the radiation pattern. That requirement significantly limits the aperture size of the array and, thus, a gain. For instance, 60 GHz or 70/80 GHz radio relay systems require the gain of 35-43 dBi that can be provided with approximately 1000-10000 antenna elements in the array. Such large-scale millimeter wave antenna arrays are not practical nowadays due to different technological constrains.
Another way is to use large aperture beam-switching antenna systems. Beam scanning in those antenna systems is achieved by a switched array disposed in a focal plane of a reflector or a lens. Known configurations of millimeter wave aperture antennas providing high gain and electronic beam steering include different reflector antennas (e.g., parabolic and Cassegrain antennas) and various types of lens antennas (e.g. thin lenses with separated feed, Fresnel lenses, Luneburg lenses, artificial lenses from reflectarrays, integrated lens antennas). In that case there is no limitations on antenna gain but the scanning efficiency is quite low. For instance, there is a small number of beam positions and consequently, limited beam scanning range, and also high losses in the switching system. Another important limitation comparing with phased antenna arrays is that the switched-beam aperture antennas are not able to combine powers from different antenna elements in space (only one element in a time moment is active). It leads to additional challenge with RF system linearity or to the need of decreasing the transmitting signal power.
Therefore, there is a need for a communication apparatus providing high antenna gain and effective beam scanning with low additional loss and capability to combine power from different antenna elements without RF linearity or transmitting power degradation. Achieving of said objects results in increasing of the effectiveness of millimeter wave communication systems in terms of maximum throughput and communication distance and also in facilitating initial antenna alignment and automatic beam re-adjustment during operation.